Field
The present invention relates to a motor control apparatus for vehicles and a current reference generation method using the same, and more particularly, to a motor control apparatus for vehicles and a current reference generation method using the same, which control a field winding type motor.
Discussion of the Background
A control system for controlling a motor (hereinafter referred to as a field winding type motor) using a winding type field is largely configured with a field circuit and a stator circuit.
The field circuit is largely configured with a field inverter and a field coil connected to the field inverter. The stator circuit is largely configured with a stator inverter and a stator coil connected to the stator inverter.
However, since the field coil of the field circuit is wound by hundreds of turns, an inductance of the field coil is high, and for this reason, a time constant of the field circuit itself is large, whereby current response characteristic is slow. Particularly, in a 48V battery system for vehicles, when a direct current (DC) link voltage is low, a field voltage capable of being applied to the field circuit is low, and for this reason, there is a limitation in increasing current control response characteristic. In order to increase the current control response characteristic, the number of turns of the field coil should be reduced, and a coil diameter should be enlarged. In this case, however, a level of a current becomes higher, and for this reason, a size of a power semiconductor of the field inverter should increase.
As described above, since the time constant of the field circuit is large, a field current flowing in the field coil is controlled to about several tens ms which is slow, and for this reason, a torque response characteristic of the motor also becomes slower. On the other hand, a d-axis and a q-axis current which flow in the stator coil of the stator circuit may be controlled to within several milliseconds (ms) which is relatively fast.
For this reason, when the field winding type motor is controlled to operate at only maximum efficiency, as illustrated in FIG. 1, a torque response is slow in a problem region “t2-t3” of a torque, and the motor cannot operate at high efficiency in a problem region “t2-t3” of the field current.